WO2006114077 discloses a conversion LED in which the converters are screen-printed onto the chip. WO2007140766 discloses a similar method.
Great efforts are currently being made to use ceramic converters for conversion LEDs. The exact positioning of said converters on the LED chip affects the reproducibility of the optical characteristics of the LED. The lateral position of a converter element on an LED chip can be captured relatively simply via cameras and used for positioning control.
The vertical position, i.e. the distance between chip and converter, is much more difficult to check. The techniques used hitherto such as screen printing involve considerable thickness variations which significantly increase the color point spread in the case of multi-fluorescent systems. Systems with separate layers of fluorescent substances of different kinds are already known per se, see e.g. EP 1 480 278 or US 2004/173806, where the longer wave fluorescent substance is also already placed closer to the chip than the shorter wave fluorescent substance. However, the thickness variation problem has so far been ignored, as no solution appeared possible.